With the growth of cloud-based services and geographically dispersed workforces, the wide area network (WAN) is the focus of increasing importance. And for good reason. It's the link that connects remote users to networked applications or cloud networks. And even though WAN speeds have increased in recent years, the WAN link is still an expensive resource and a likely bottleneck when trying to provide remote users with good response times.

Enter WAN optimization. Typically implemented using a pair of systems -- one located at the central site and one at the remote site -- WAN optimization devices use a variety of techniques to make your sessions run faster.

WAN optimization: What makes it work

If your organization is in the market for WAN optimization tools and appliances, understand conceptually how they operate to select the best WAN optimization system for your needs.

There are fundamental capabilities and features each WAN optimization system should provide.

In a nutshell, WAN optimization products use a variety of techniques to do two things: reduce the amount of data that has to traverse the WAN and accelerate whatever traffic remains. Reducing the amount of data that must traverse the WAN also cuts protocol delays. The combination decreases latency and allows the existing WAN link to be used more efficiently.

Unfortunately, reading most vendor WAN optimization marketing materials won't help you understand what you need. Where LAN switches are built almost exclusively around industry-standard specifications (e.g., IEEE 802.1Q VLANs, 802.1p prioritization, etc.), WAN optimization devices are above the virtual timberline when it comes to industry standards. Simply put, there aren't really any.

That said, there are fundamental capabilities and features each WAN optimization system should provide, and to ensure your WAN optimization tools' deployment does the trick, look for information on the following:

WAN optimization: Must-have capabilities

Compression. A simple way to optimize your WAN is to scan the data packets in real time and compress the data before sending it across the network. When the associated WAN optimization device receives it on the other end, the data is uncompressed and passed on to the target server via the local area network.

While the compression/decompression functions take time, latency is decreased by the fact that the actual amount of traffic traversing the WAN is reduced.

Of course, the size of benefit you receive depends on your traffic. If your data consists of alphanumeric data with repeated characters or spaces, you are virtually guaranteed benefits. On the other hand, if you are sending backup data that has been compressed before transmission (e.g., .zip archive files), WAN optimization compression probably won't help you. In fact, if the WAN optimization device blindly tries to compress everything, you might even see performance suffer. That's because you will incur latency as the WAN device tries to compress -- but doesn't succeed -- in shrinking your payload in any appreciable way.

Deduplication/Caching. A step up in sophistication from compression alone, deduplication and caching can provide an even more dramatic reduction in data traversing the WAN -- along with commensurate improvement in response time. While implementations certainly vary, the basic idea is that "chunks" of data can be identified and tagged by the WAN optimization system.

Once that chunk -- the nature of which is system dependent -- has been sent across the WAN once, it need not be sent again. The WAN optimization device simply sends the tiny tag across the WAN to the partner system at the other end. The receiving system then grabs the data represented by the tag out of its cache and inserts that into the packet before delivering it to the receiving LAN.

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With the generally low price of memory and solid-state drives, a lot of data can be stored in this manner. The benefit will be directly related to how much repeated data occurs in your WAN traffic. It stands to reason that deduplication can only help when there are duplicates to deal with. Caching is essentially another term for deduplication in this context.

TCP session optimization. Even when you reduce the amount data flowing across the WAN, throughput and response time are often degraded by inefficiencies in the TCPI/IP protocol.

At the risk of oversimplification, there can be significant "wait" time during a session as one end awaits confirmation of receipt from the other. The TCP "windows" allow multiple packets to be sent before waiting. Still, when the maximum number of packets is sent, the sender must stop and wait.

Leaving the WAN idle and unused can degrade end-user performance in much the same way that having an over-committed WAN affects response time.

WAN optimization appliances can insert themselves into the protocol by intercepting these window acknowledgements, among other things. This reduces or eliminates the time wasted waiting for the acknowledgment to arrive from the other end of the WAN.

WAN optimization performance depends on your network traffic

As with other features, the benefit that you will see depends upon your application. Chatty or interactive applications -- like ones that involve ordering or searching -- typically send small packets containing the requests for information. Each packet exchange can involve waiting for the TCP protocol to acknowledge the packet. WAN optimization platforms intercept and proxy those exchanges to reduce application wait times and improve performance.

Ultimately, each optimization tool is designed to mitigate specific attributes of your traffic. If your traffic doesn't fit the profile, your benefit could be minimal.

So when you see vendor claims of "up to 99% data reduction," it is very much a statement that is always followed by the technical equivalent of "your mileage may vary." In the end, it's all about your traffic.

Now that you know about techniques used by WAN optimization vendors to accelerate your applications, you are halfway there. Since the effectiveness of these techniques depends on the nature of your particular application and application data, the selection process has to move beyond a mere checklist. In our upcoming companion article, we walk you through the process of setting up a microcosm of your application environment in a demo lab to determine, empirically, the benefits of a given optimization product.

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